Regulation tennis rackets are comprised of a handle having a frame at one end. Strings are strung in the frame such as to form a grid pattern where one row of strings would be in a uniformly spaced pattern and parallel to each other and perpendicular thereto would be another set of parallel strings which are spaced apart the same distance from one another. Furthermore, each string is grouped over and under each string it meets. This grid pattern produced creates more resilience toward the center or "sweet spot" in the racket frame. The regulation or traditional strung racket filament is circular in cross-section. As a result, both hitting faces of the racket will have identical playing characteristics.
The Delorean U.S. Pat. No., 3,962,431, shows a type of filament string which is triangular in cross-section and strung such that the apex of the triangle forms one face and the base of the triangle forms the other face of the racket. Furthermore, in Delorean the roughness or texture of one face can be altered. With this type of filament string, the hitting characteristics of the racket are different.
In Henry U.S. Pat. No. 4,005,863 the filament is square, hexagonal, triangular or oval in cross-section and the filaments are extruded in such a manner as to form a natural helix or twist to the filament in a natural manner. Again, the hitting surface as a result of these types of strings will markedly affect the playing characteristic of the racket.